I would have to say there are several dives, one was in Cayman Brac that we spent a dive with a dolphin that let us touch it, another was the night dive with the Mantas, another was Kilibob's near the Father's reef off New Britain/PNG, and another was Steve's Bommie when a Minke whale swam underneath me in Australia. Then there's the one in the Red Sea when we encountered a hugh Napolean wrasse, and the one off South Africa in the Indian Ocean when my wife signals shark and I turn around to see a shark about 14 ft. long.......I guess I could on and on. To say one was the greatest would be very difficult.